Telecoms giant BT took its first big step back into the mobile phone market today as it launched a new business service aimed at delivering fixed line and mobile calls to the same handset.

It currently has just 1% of the corporate mobile market but said it now plans to grow "aggressively".

The BT One Phone service is designed to ensure that businesses never miss a call.

BT said research showed 60% of calls to company mobiles were answered in the office, but figures showed 90% of users were unhappy with the call quality of mobile phones.

It plans to address this by installing private mobile phone networks at business sites to provide fixed line quality coverage for a handset that will be able to be taken out and away from the building by employees.

Outside the office these will connect to a mobile network, through a deal BT signed with operator EE earlier this year.

The service is being offered from today with a national roll-out over the next six months.

It is the first step in BT's re-entry in the mobile phone market following the demerger of its BT Cellnet business in 2001 which was later bought by Telefonica to become O2.

It plans to launch a mobile phone business for the wider public by the end of the current financial year.

BT said the new business service would work with a full range of mobile phones by inserting a One Phone SIM.

Combined with 4G and unlimited access to millions of BT Wi-Fi hotspots, it would enable employees to "be as productive outside the office as they are at their desk".

BT Business chief executive Graham Sutherland said: "With an increasingly mobile and demanding workforce, businesses need communications technology that is as flexible as they are.